Performance: Load Only Necessary Modules On setup and requiring API

[alex-courtis]

User requiring api.lua or executing setup results in most modules being required. This has a cost ~7-11ms.

See #3229 for background and timing experiments.

Only the following are absolutely required when executing setup for the first time:

008.600  000.064  000.064: require('nvim-tree.log')
008.825  000.224  000.224: require('nvim-tree.utils')
010.094  000.060  000.060: require('nvim-tree.notify')
010.097  000.147  000.087: require('nvim-tree.legacy')
012.854  000.063  000.063: require('nvim-tree.commands')

api.lua does not need to contain any requires barring notify; they can be lazily evaluated on calling the API.

This is long overdue and will greatly ease #2908

Implementation Plan

• 1 - nvim-tree.lua Move all functions that do not relate to setup into another module. This is not API so we may refactor at will.
• 2 - api.lua move all requires inline. This is a messy and undesirable solution, however it will be resolved during Documentation: Opts luals Annotations #2934 and Multi Instance: Help #2908
• 3 - Create a new options module that contains user setup options, set during setup. This will allow us to remove the setup calls for non-class modules; they can require and read from the configuration module.
• 4 - Remove M.setup call, retrieving options from the new options module
  • actions/fs
  • actions/node
  • actions/root
  • actions/tree
  • buffers.lua
  • diagnostics.lua
  • explorer/watch.lua
  • git/utils.lua
  • help.lua
  • keymap.lua
  • lib.lua
  • notify.lua
  • renderer/components
  • view.lua
  • watcher.lua

These should be executed in separate PRs as there is a large blast radius. 1 should be broken down into small PRs to ameliorate risk and allow fast rollback.